1. Field of the Invention
The present invention relates to a plasma display panel, and more particularly, to the structure of a plasma display panel.
2. Description of the Background Art
In general, in a plasma display panel, a barrier rib formed between an upper panel and a lower panel forms one unit cell. Each cell is filled with an inert gas comprising a primary discharge gas, such as neon (Ne), helium (He) or a mixed gas of Ne+He, and a small amount of xenon (Xe). If the inert gas is discharged with a high frequency voltage, it generates vacuum ultraviolet rays. Phosphors formed between the barrier ribs are excited to implement images.
More particularly, a three-electrode AC surface discharge type plasma display panel has advantages of lower voltage driving and longer product lifespan since wall charges are accumulated on a surface upon discharge and electrodes are protected from sputtering generated by a discharge.
FIG. 1 illustrates the structure of a plasma display panel in the related art.
Referring to FIG. 1, the discharge cell of the plasma display panel in the related art comprises scan electrodes Y and sustain electrodes Z formed on a bottom surface of an upper substrate 10, and address electrodes X formed on a lower substrate 18. The scan electrode Y comprises a transparent electrode 12Y, and a metal bus electrode 13Y, which has a line width smaller than that of the transparent electrode 12Y and is disposed at one side edge of the transparent electrode. Furthermore, the sustain electrode Z comprises a transparent electrode 12Z, and a metal bus electrode 13Z, which has a line width smaller than that of the transparent electrode 12Z and is disposed at one side edge of the transparent electrode.
The transparent electrodes 12Y, 12Z are generally formed of Indium Tin Oxide (ITO) and are formed on a bottom surface of the upper substrate 10. The metal bus electrodes 13Y, 13Z are generally formed of metal such as chromium (Cr) and are formed on the transparent electrodes 12Y, 12Z. The metal bus electrodes 13Y, 13Z serve to reduce a voltage drop caused by the transparent electrodes 12Y, 12Z having high resistance. On the bottom surface of the upper substrate 10 in which the scan electrodes Y and the sustain electrodes Z are formed parallel to each other is laminated an upper dielectric layer 14 and a protection layer 16. Wall charges generated during the discharge of plasma are accumulated on the upper dielectric layer 14. The protection layer 16 functions to prevent the upper dielectric layer 14 from being damaged by sputtering generated during the discharge of plasma and also to improve emission efficiency of secondary electrons. Magnesium oxide (MgO) is generally used as the protection layer 16.
A lower dielectric layer 22 and barrier ribs 24 are formed on the lower substrate 18 in which the address electrodes X are formed. A phosphor layer 26 is coated on the surfaces of the lower dielectric layer 22 and the barrier ribs 24. The address electrodes X are formed to cross the scan electrodes Y and the sustain electrodes Z. The barrier ribs 24 are formed parallel to the address electrodes X and function to prevent ultraviolet generated by a discharge and a visible ray from leaking to neighboring discharge cells. The phosphor layer 26 is excited with an ultraviolet generated during the discharge of plasma to generate any one visible ray of red, green and blue. An inert mixed gas is injected into discharge spaces provided between the upper substrate 10 and the barrier ribs 24 and between the lower substrate 18 and the barrier ribs 24.
FIG. 2 illustrates a method of implementing images of the plasma display panel in the related art.
As shown in FIG. 2, in the plasma display panel, one frame period is divided into a plurality of sub-fields having a different number of discharges. The plasma display panel is excited in a sub-field period corresponding to a gray level value of an input image signal, thereby implementing images.
Each sub-field is divided into a reset period for uniformly generating a discharge, an address period for selecting a discharge cell and a sustain period for implementing gray levels depending on the number of discharges. For example, if it is sought to display images with 256 gray levels, a frame period (16.67 ms) corresponding to 1/60 seconds is divided into eight sub-fields, as shown in FIG. 2.
Each of the eight sub-fields SF1 to SF8 is again divided into a reset period, an address period and a sustain period. In this case, the sustain period increases in the ratio of 2n (where, n=0,1,2,3,4,5,6,7) in each sub-field. As described above, since the sustain period is varied in each sub-field, gray levels of images can be represented.
In the plasma display panel driven as described above, a versatile front filter is disposed on the upper substrate 10. In the related art, the front filter has been used in order to accomplish objects, such as Electromagnetic Interference (hereinafter referred to as “EMI”) shielding, Near Infrared Rays (hereinafter referred to as “NIR”) shielding, improved color purity and prevention of the reflection of external light. Since the front filter in the related art consists of a number of layers, however, a problem arises because the front filter has a predetermined or higher thickness. More particularly, the NIR shielding film included in the front filter is difficult to form using only a NIR shielding material. Therefore, there are problems in that the process time is long and the manufacturing cost is high.